A general goal in the field of lock manufacture is to provide improvements in several specific characteristics of the locks and the keys associated therewith, particularly including increasing the level of difficulty of making unauthorized copies of keys and of determining the tumbler arrangement from the key itself; minimizing the overall size of the lock; providing a lock type which has a large number of possible tumbler permutations and, therefore, the possibility for a large number of different key arrangements; providing a lock which is extremely difficult to open without use of a key; and providing a lock which can be manufactured without the expense and difficulty of extremely fine tolerances and without the requirement for overly complex machines or processes for either the lock or the key production. The prior art includes numerous examples of the efforts which have been made in this field in the past.
OS No. 2,546,550 discloses a lock cylinder with a flat key constructed as a pronged bit key in which, in a known manner, closing notches run at right angles to the key shank over the complete narrow side of the key facing away from the key back in such a way that the planar, rectangular notch base faces extend perpendicular to the longitudinal direction of the key shank over the entire narrow side of the key and terminate at the two flat sides therof. In addition, the planar closing notch base faces are inclined at an angle with respect to the key shank median longitudinal plane at an angle, so that the distances of the notch base faces from the key back are greater on one wide side of the key than the corresponding spacing on the other wide side of the key. In addition, the key bow or handle is displaced by a small angle relative to the key shank. The lock slot is inclined by the same angle, so that when the key is inserted, the key bow is in a vertical plane, so that the inclined positions of the key shank and the lock slot are not visible.
The inclined position of the base faces of the recesses, together with the inclined arrangement of the slot in the lock in particular increase manufacturing costs. However, this construction scarcely increases the security against illegal or unauthorized copying of the key.
In another known cylinder lock with a flat key of this general type, shown in German GM No. 7,818,276, each of the two flat sides of the key is associated with a row of tumblers, and the two tumbler planes are inclined in opposite directions by identical angles relative to, in each case, the associated effective lateral surface of the inserted flat key. In addition, in the case of this known cylinder lock two rows of tumblers are associated with one of the two narrow sides of the flat key, and the two tumbler planes are inclined in opposite directions with respect to the median longitudinal plane of the inserted flat key. The two axial planes of the recesses of the two rows of depressions running in the longitudinal direction of the key are inclined in accordance with the slope of the two tumbler planes in opposite directions with respect to the median longitudinal plane of the flat key.
As a result of the large number of rows of tumblers, in the case of this known cylinder lock with a flat key, not only is the security against illegal opening of the lock increased, but particularly due to the inclination of the recesses relative to the key surface, the illegal copying of the key is made more difficult and in addition the number of permutation or combination possibilities available with lock is increased. However, the necessary external diameter of the lock cylinder and, consequently of the complete cylinder lock is still relatively large. Furthermore, the manufacturing tolerances for manufacturing the lock are correspondingly high, so that the security against illegal copying of the key still leaves much to be desired.
DAS No. 1,553,294 describes and shows a tumbler arrangement for the pin tumblers in a rotary cylinder lock, on whose flat key are provided additional recesses for pin tumblers inclined by an angle of 45.degree. relative to the side face of the key, besides the conventionally provided recesses for the perpendicular pin tumblers on the side face of the inserted key. However, the narrow sides of the key are left smooth.
In the case of this lock or the associated key, the manufacturing costs, due to the complicated processing machines and the necessity of maintaining close tolerances, are far too high when compared with the achievable increase in security against copying the key.